In industrial series production requiring implementation of a plurality of repetitive assembly operations, e.g. tightening nuts and bolts, it has become customary to automate the operations involved, i.e. tightening nuts and bolts as far as possible by employing automated tools. For example, a process system including a plurality of automated nut runners is lowered onto an cylinder head for bolting it down to the cylinder block in accordance with a predefined program. In this arrangement a process parameter programming means sets, among other things, each of the nut runners to a specific torque and/or torsion angle for tightening the individual bolts. Thus, by automatically marrying the cylinder blocks and cylinder heads, together with the process system, highly automated series production is achievable. In this case the process system itself is designed to customer specifications, i.e. the process system is tailored to the process operation to be implemented in each case so that, for example, any change in the shape of the workpieces, in this case the cylinder heads, a new process system needs to be designed.
On the other hand, there are process operations which permit handling by automated or robotic devices either not at all or only with difficulty. In addition, process operations exist for which, due to the timing cycle involved, automated assemblies cannot be put to use and thus single or multiple screw drivers or nut runners and other process tools are required for manual guidance. Thus, such process operations, in series production too, require the use of, for example in bolting, such tools as e.g. poke, offset or gunning screw drivers or nut runners or other manually guided multiple screw drivers or nut runners. Process tools of this type are likewise highly automated so that for each process operation, e.g. bolting operation, the torque and/or the torsion angle is set by a process parameter programming means and the torque and/or torsion angle measured during bolting, which is not completed until the actual parameters agree with the programmed parameters.
It will readily be appreciated that employing such a manually guided process tool permits more flexibility in use since it merely needs to be provided with a suitable adapter bush, after which a process operation can be implemented, i.e. such a process tool is not tailored to a specific workpiece, e.g. to a cylinder head, but can be put to use for any number of different process operations.
Whilst, however, it is assured with a process system tailored to a specific workpiece, as described above, that all process sites (bolting sites) are processed (bolted), problems materialize as regards process assurance when making use of a manually guided, partly automated process tool, as will be explained in the following.
In considering the case, for example, in which an adapter bush already preassembled with some parts arrives in a predefined process station, i.e. an assembly station of an automobile production line, it will firstly be assumed—although, of course, the automobile body is moved at a certain speed—that the body is stationary or at least relatively stationary in the process station. Since automobile bodies may be subject to different standards, for example a US version or EU version, the controller controlling the individual process tools is first programmed to basic data, as recorded, for example, on a production card attached to the body. At this point in time the controller and thus the process tool “see”, for example, that ten different M10 bolts and fifteen M15 bolts need to be tightened. An operator thus takes an M10 adapter bush from the crib (as is also indicated optically on the crib) and implements ten times a process operation for tightening M10 nuts/bolts with the torque and/or torsion angle as programmed in each case. Once the controller has “seen” that 10 process operations have been implemented with M10 it enables the next size M15 for the corresponding number of process operations in each case. However, all that this assures is that a predefined number of process operations is implemented. It does not assure these are actually done at the corresponding process sites (assembly sites). In other words, the operator needs to strictly adhere to a predefined sequence since this is the only way of assuring that always the corresponding process site is processed with the correct process parameters.
As already mentioned, however, the body is not stationary in the process station, it instead being moved at a certain speed. This adds to the problem as explained above. For example, the operator may have already processed a few assembly sites on the next body, so that although the predefined number of bolting operations has been implemented, there is the problem of complete processing getting out of step and thus there is no longer the assurance that all bolts really have been tightened and/or with the corresponding torque/torsion angle (since there may be a change too, in the torque/torsion angle for each process operation and workpiece). This is basically a problem since predefining the torque/torsion angle in conjunction with the number of process operations is independent of the location of the process tool, it depending solely on the sequence in processing or the predefined number of operations.